Start practicing

Prosthodontics & Occlusion · single question

A porcelain-fused-to-metal crown appears excessively opaque and lifeless. All of the following contribute to this appearance EXCEPT:

  1. Adequate (generous) axial and incisal reduction
  2. A thick metal substructure
  3. Insufficient tooth reduction leaving too little space for porcelain
  4. Excessive thickness of the opaque porcelain layer
Show answer and explanation

Correct answer: A. Adequate (generous) axial and incisal reduction

  • A. Correct — this is the EXCEPTION. GENEROUS reduction provides the 1.5–2.0 mm of space needed to layer opaque, dentine and enamel porcelains in proper proportion. Adequate space is what PREVENTS opacity; it does not cause it.
  • B. Incorrect (this DOES cause opacity). A bulky metal coping consumes the available space, leaving too little room for the translucent dentine and enamel layers, so the opaque shows through.
  • C. Incorrect (this DOES cause opacity). Under-preparation is the single most common clinical cause — the technician is forced to place opaque and body porcelain in a thin layer with no room for translucency, giving a flat, chalky, monochromatic result.
  • D. Incorrect (this DOES cause opacity). Opaque porcelain exists only to mask the metal; if applied too thickly it dominates the optical result and blocks the depth normally created by the overlying layers.

Practice Prosthodontics & Occlusion questions Prosthodontics & Occlusion study notes

More Prosthodontics & Occlusion practice questions